¿Campos de formulario obligatorios?

[hermanosvalor]

<td width="20%" align="right"><font face="Arial" color="#000000"><small>E-mail</small></font></td>
<td width="30%"><font color="#FFFFFF" face="Arial"><input type="text" name="Email"
size="20"></font></td>
</tr>
<tr>
<td width="20%" align="right"><font face="Arial" color="#000000"><small>Teléfono </small></font></td>
<td width="30%"><font color="#FFFFFF" face="Arial"><input type="text" name="Telefono"
size="20"></font></td>
<td width="20%" align="right"><font face="Arial" color="#000000"><small>(*) Fax</small></font></td>
<td width="30%"><font color="#FFFFFF" face="Arial"><input type="text" name="Fax" size="20"></font></td>
</tr>
<tr>
<td width="20%" align="right"></td>
<td width="30%"></td>
<td width="20%" align="right"><font face="Arial" color="#000000">  </font></td>
<td width="30%"></td>
</tr>
<tr>
<td width="20%" align="right"><font face="Arial" color="#000000"><small>Empresa& lt;/small></font></td>
<td width="30%"><font color="#FFFFFF" face="Arial"><input type="text" name="Empresa"
size="20"></font></td>
<td width="20%" align="right"><font face="Arial" color="#000000"><small>(*) Dirección</small></font></td>
<td width="30%"><font color="#FFFFFF" face="Arial"><input type="text"
name="DireccionEmpresa" size="20"></font></td>
</tr>
<tr>
<td width="20%" align="right"><font face="Arial" color="#000000"><small>(*) Teléfono</small></font></td>
<td width="30%"><font color="#FFFFFF" face="Arial"><input type="text"
name="telefonoEmpresa" size="20"></font></td>
<td width="20%" align="right"><font face="Arial" color="#000000"><small>(*) Fax</small></font></td>
<td width="30%"><font color="#FFFFFF" face="Arial"><input type="text" name="FaxEmpresa"
size="20"></font></td>
</tr>
<tr>
<td width="20%" align="right"><font face="Arial" color="#000000"><small>(*) E-mail</small></font></td>
<td width="30%"><font color="#FFFFFF" face="Arial"><input type="text" name="EmailEmpresa"
size="20"></font></td>
<td width="20%" align="right"></td>
<td width="30%"></td>
</tr>
<tr>
<td width="20%" align="right"></td>
<td width="30%"></td>
<td width="20%" align="right"></td>
<td width="30%"></td>
</tr>
<tr>
<td width="20%" align="right"><font face="Arial" color="#000000"><small>Tarjeta de Credito</small></font></td>
<td width="30%"><font color="#FFFFFF" face="Arial"><select name="Tarjeta" size="1">
<option value="Amex">Amex</option>
<option value="Visa">Visa</option>
<option value="Mastercard">Mastercard</option>
<option value="Diners">Diners</option>
</select></font></td>
<td width="20%" align="right"><font face="Arial" color="#000000"><small>Nombre del Titular</small></font></td>
<td width="30%"><font color="#FFFFFF" face="Arial"><input type="text" name="NombreTitular"
size="20"></font></td>
</tr>
<tr>
<td width="20%" align="right"><font face="Arial" color="#000000"><small>Numero&l t;/small></font></td>
<td width="30%"><font color="#FFFFFF" face="Arial"><input type="text" name="NumeroTarjeta"
size="20"></font></td>
<td width="20%" align="right"><font face="Arial" color="#000000"><small>Código de
seguridad</small></font></td>
<td width="30%"><font color="#FFFFFF" face="Arial"><input type="text" name="Codigo"
size="5"></font></td>
</tr>
<tr>
<td width="20%" align="right"><font face="Arial" color="#000000"><small>(*) Fecha de
vencimiento</small></font></td>
<td width="30%"><font color="#FFFFFF" face="Arial"><input type="text"
name="VencimientoMes1" size="2"> / <input type="text" name="Vencimientoano1" size="2"></font></td>
<td width="20%" align="right"></td>
<td width="30%"></td>
</tr>
<tr>
<td width="20%" align="right"></td>
<td width="30%"></td>
<td width="20%" align="right"></td>
<td width="30%"></td>
</tr>
<tr>
<td width="100%" align="center" colspan="4"><div align="center"><center><tabl e border="0"
width="100%" cellspacing="15" cellpadding="0">
<tr>
<td width="100%"><div align="center"><center><p&gt ;<font face="Arial" color="#000000"><small><inpu t
TYPE="button" VALUE="Enviar" onClick="Validar(this.form)"><inpu t TYPE="reset"></small></font></td>
</tr>
</table>
</center></div></td>
</tr>
</table>
</center></div>
</form>